There are various types of pneumatic tires which are designed to be capable of running continuously for a certain distance even after the tires are punctured. Among those, there are types in which an inner circumferential surface of a tire is supported in a case of puncture by a ring-shaped support member arranged in an inner space of the tire. What are widely known as these types include: a type in which a run-flat support body is arranged inside a tire; and a type in which an air bladder made of a circular ring-shaped film body is inserted inside a tire.
Out of these types of tires, in the type in which an air bladder made of a circular ring-shaped film body is inserted inside a tire, the internal pressure of the air bladder is generally set equal to or higher than that of the pneumatic tire. The air bladder is configured to change its shape by expanding its diameter, and thus supports load when the internal pressure of the tire becomes lower as a result of the tire's puncture. To this end, a material with low air permeability such as butyl rubber is used for the film body constituting the air bladder. Moreover, a design which enables the durability to be secured for run-flat running is applied. A proposal has been heretofore made for a configuration of the film body of the air bladder, in which a reinforcement cord layer is arranged on the outer circumferential wall of the film body (see Patent Document 1). Another proposal has been made for a configuration of the film body, in which a rigid plate is arranged on the outer circumferential surface of the film body (see Patent Document 2).
However, both proposals have a problem that the arrangement of the reinforcement cord layer or the rigid plate increases the mass of the tire, and a demand for lower fuel consumption cannot be accordingly satisfied. In addition, there is a problem that it is difficult to maintain the internal pressure of the air bladder for a long period of time, and decrease in the internal pressure of the air bladder accordingly results in decrease in the run-flat durability.